1. Field of the Invention
The present invention relates to a layer 2 switch (hereinafter, referred to as L2 switch), and in particular to an L2 switch having a VLAN function for configuring a layer 2 network in a star topology, a mesh topology, a ring topology, or the like.
In recent years, as the speed of data communications is increased, demands for a layer 2-based service which is inexpensive and easy to control have been increasing. In the layer 2 service, reliability with assured bandwidth is important in the same way as in, for example, an SDH/SONET transmission apparatus, a WDM apparatus and an ATM apparatus applied in conventional leased line services.
2. Description of the Related Art
The specification of the Ethernet interface is generally a best-effort type. Therefore, in e.g. an Ethernet leased line service using a conventional L2 switch/bridge or a router including a bridge, a frame discard processing occurs unconditionally when a congestion occurs.
Accordingly, it has been required to assure a bandwidth where no congestion occurs in order to guarantee a bandwidth. Also, a link down transfer per user (VLAN) set on an L2 network could not be performed.
Thus, e.g. a layer 2-based Ethernet leased line service has been inadequate for implementation intended for a communication common carrier because the bandwidth could not be effectively utilized and the link down transfer could not be performed.
Therefore, the conventional Ethernet leased line service has been an expensive one composed of two types of platforms including a WDM apparatus, an SDH/SONET transmission apparatus or an ATM apparatus, capable of assuring a bandwidth and highly reliable but highly priced per apparatus, as a relaying apparatus; and an L2 switch/router as an Ethernet interface. Otherwise, the conventional Ethernet leased line service has been a service using a conventional L2 switch/router unable to effectively utilize the bandwidth and impossible to perform a link down transfer.
Moreover, an existing layer 2 switch/router has no function of transferring a link disconnection of an interexchange channel. Accordingly, in order to recognize the disconnection of the interexchange channel, a user himself or herself is required to always confirm the state of the channel by using e.g. a Hello packet or the like.
Namely, problems of e.g. the layer 2-based Ethernet leased line service are that the network is made expensive by using the SDH/SONET transmission apparatus, the ATM apparatus or the WDM apparatus, and that in the layer 2 service applied by the existing communication common carrier, it is unable to effectively utilize the bandwidth and impossible to perform the link down transfer per user (VLAN).